Two-pass reports

The report engine supports two-pass reports, to order rows automatically.

The one-pass report requires sorted data to be produced by the report driver in order to handle BEFORE/AFTER GROUP OF blocks properly. The two-pass report handles sorts internally and does not need sorted data from the report driver. During the first pass, the report engine sorts the data and stores the sorted values in a temporary file in the database. During the second pass, it calculates any aggregate values and produces output from data in the temporary files.

A report is defined as a two-pass report if it includes any of the following items:

An ORDER BY section without the EXTERNAL keyword.
The GROUP PERCENT(*) aggregate function anywhere in the report.
Any aggregate function that has no GROUP keyword in any control block other than ON LAST ROW.

Two-pass reports create temporary tables. The FINISH REPORT statement uses values from these tables to calculate any global aggregates, and then deletes the tables. Since two-pass reports create temporary tables, the report engine requires a database connection, and the database server must support temporary tables with indexes.

Consider avoiding two-pass reports when a regular report is possible.